1. Field of the Invention
The present invention relates to a charged beam exposure apparatus, a charged beam exposure method, a method of manufacturing a mask, and a method of manufacturing a semiconductor device, which are used in semiconductor process.
2. Description of the Related Art
As one of lithography processes in semiconductor manufacturing processes, there is a photolithography process. The photolithography process has advantages including an easy-to-use process, a low cost performance, and the like. Therefore, the photolithography process is used widely in device production.
In the photolithography process, innovations are always made continuously. For example, in recent years, ultrafine elemental devices of a 0.1 μm level have been nearly attained through the introduction of a short wavelength (adaptation of an ArF excimer laser light source). For further ultrafine elemental devices, an immersion exposure apparatus in which a region between an objective lens and a surface of sample is immersed in liquid has been under its development. This type of exposure apparatus is expected to become a mass production lithography tool for the 65 nm rule generation.
However, in realizing the immersion exposure apparatus, the time concerning the development of the next-generation lithography technology has been prolonged, and it is worried that it may not catch up with the speed of miniaturization of devices.
On the other hand, it has been substantiated that an electron beam (EB) lithography process enables processing down to 10 nm by use of a thin narrowed electron beam. From the viewpoint of the miniaturization, the process will not have problems for some time to come. Nevertheless, concerning the dimensional precision and positional precision of drawn patterns, the process has the following problem. That is, the process has the problem that there occur a beam dimension error and a beam exposure position error depending on the cross-sectional area of the electron beam.
In an electron beam drawing apparatus of a variably shaped beam type, an electron beam is emitted from an electron gun. The electron beam passes through the first shaping aperture mask. The electron beam having passed through the first shaping aperture mask is irradiated onto the second shaping aperture mask. Dimensions of the beam that reaches onto a sample through the second shaping aperture mask is controlled by controlling a position of the beam that is irradiated onto the second shaping aperture mask.
When a fine pattern is drawn, in other words, when a fine beam is irradiated onto the sample, most of the electron beam is cut by the second shaping aperture mask. Therefore, most of the electron beam energy is absorbed in the second shaping aperture mask.
On the other hand, when a large area pattern is drawn, in other words, when a large area beam is irradiated onto the sample, the amount of the electron beam cut by the second shaping aperture mask is extremely small. Therefore, only a little amount of the electron beam energy is absorbed in the second shaping aperture mask.
Thus, in the case of drawing the fine pattern, the amount of the electron beam energy that is absorbed into the second shaping aperture mask is larger than in the case of drawing the large area pattern. Accordingly, the heat quantity that is given to the second shaping aperture mask becomes larger in the case of drawing the fine pattern than in the case of drawing the large area pattern. Therefore, the thermal expansion of the second shaping aperture mask becomes larger in the case of drawing the fine pattern than in the case of drawing the large area pattern.
Such the difference in the heat quantity absorbed in the second shaping aperture mask causes temperature fluctuation in the second shaping aperture mask, and as a result, thermal expansion changes occur in the second shaping aperture mask. Then, owing to such thermal expansion changes, a position of an opening (aperture) in the second shaping aperture mask changes, and in a conspicuous case, there occurs a distortion in the opening shape. These changes of the opening position and the distortion of the opening shape become factors to cause a dimension error of the electron beam which passes through the second shaping aperture mask or an irradiation position error of the electron beam on a sample (Japanese Patent No. 3431445).
Also, even in the case of a character projection type (partial entire exposure type) exposure apparatus or an electron beam projection lithography (EPL) type exposure apparatus (large area transfer exposure apparatus) that transfers a mask pattern by use of an electron beam, there occur similar problems.
More specifically, the heat quantity that the electron beam supplies to a mask differs due to differences in an opening ratio of a partial entire exposure transfer mask (character aperture mask), and an opening ratio of an EPL mask, and accordingly, temperature fluctuations occur in the mask during exposure. As a result, there occurs a change in the thermal expansion of the mask, and a position of the opening in the mask changes, and in a conspicuous case, there occurs a distortion in the opening shape. These changes of the opening position and the distortion of the opening shape become factors to cause a dimension error of a transferred pattern (for example, a resist pattern) on a wafer or an irradiation position error of the electron beam on a wafer.